Words Worth Knowing- The Structure of the Human Eye

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white, opaque, and tough covering of the eye that protects it; nourished by capillaries that supply oxygen to it (red squiggly lines that are visible on the whites of your eyes)

clear and transparent; positioned in front of the pupil and iris and protects them; nourished by aqueous humor and tears produced by lacrimal glands

lacrimal glands
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located above each eye in the upper lid; secretes fluid (tears) to lubricate and moisten the surface of the eye

circular muscles surrounding the pupil; helps regulate amount of light entering the eye; different colors due to lack or concentration of melanin (pigment)

opening in the middle of the eye; regulates amount of light entering the eye with the help of the iris; sensitive to light

ciliary muscles
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these muscles around the lens hold it in place and change its shape to adjust to focus on objects at different distances

acqueous humor
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clear, watery fluid behind the cornea; nourishes the cornea and works with it to help focus light

colorless; nearly transparent; focuses light rays onto retina; behind iris and pupil; ciliary muscles contract, lens thickens, focus on near objects; muscles relax, lens flattens, focus on far objects

vitreous humor
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clear, jelly-like fluid; holds internal structure in place; gives shape to the eye ball; fills up posterior chamber

thin, innermost layer; sensitive to light; absorbs light entering the eye

second layer between sclera and retina; contains blood vessels to nourish retina

concentration of cone cells; processes clear sharp vision; located in the center of the retina

dip in macula; only cone cells; highest sensitivity

optic disk
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all, white, oval-shaped area on the retina; beginning of the optic nerve

blind spot
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the optic disk; called the "blind spot" because the area is absent of photoreceptors to images cannot be processed in this area

optic nerve
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begins at optic disk, located at the back of the eye; carries sensory information from retina's photoreceptors to visual centers of the brain


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